What s the Internet? PC server laptop cellular handheld access points wired s connected computing devices: hosts = end systems running apps communication s fiber, copper, radio transmission rate = bandwidth s: forward packets obile Home Global Regional Institutional What s the Internet? Protocols control sending and receiving TCP, IP, HTTP, Internet: of s Internet standards RFC: Request for comments IETF: Internet Engineering Task Force obile Global Home Regional Institutional Introduction 1-1 Introduction 1-2 What s the Internet? Service view: What s a protocol? distributed s: Web, VoIP, email, games, e-commerce, file sharing communication services provided to apps: reliable data delivery best effort (unreliable) data delivery human protocols: what s the? I have a question introductions protocols: protocols define format, order of msgs sent and received among entities, and actions taken on msg transmission, receipt machines rather than humans all communication activity in Internet governed by protocols Introduction 1-3 Introduction 1-4 What s a protocol? A closer look at structure: a human protocol and a computer protocol: Hi Hi Got the? 2:00 TCP connection request TCP connection response Get http://www.awl.com/kurose-ross <file> Introduction 1-5 edge: s and hosts access s, media: wired, communication s core: interconnected s of s Introduction 1-6 1
The edge: end systems (hosts): run programs e.g. Web, email at edge of client/server model client host requests, receives peer-peer service from always-on server client/server e.g. Web browser/server; email client/server peer-peer model: minimal (or no) use of dedicated servers e.g. Skype, BitTorrent Access s and media Q: How to connect end systems to edge? residential access nets institutional access s (school, company) mobile access s Introduction 1-7 Introduction 1-8 Internet access Wireless access s 100 bps 100 bps 100 bps switch 1 Gbps server institutional to institution s access via base station aka access point LANs: 802.11 wider-area access provided by telco operator 3G, 4G base station typically used in companies, universities, etc 10 bps, 100bps, 1Gbps, 10Gbps end systems typically connect into switch mobile hosts Introduction 1-9 Introduction 1-10 Home s Physical edia Typical home components: DSL or cable modem /firewall access point to/from cable headend cable modem / firewall access point laptops : what lies between transmitter & receiver guided media (cables): signals propagate in solid media: copper, fiber, coax unguided media: signals propagate freely, e.g., radio Twisted Pair (TP) two insulated copper wires Category 3: traditional phone wires, 10 bps Category 5: 100bps Introduction 1-11 Introduction 1-12 2
Physical edia: coax, fiber Physical media: radio Coaxial cable: two concentric copper conductors Fiber optic cable: high-speed operation: high-speed point-to-point transmission (e.g., 10 s- 100 s Gpbs) low error rate repeaters spaced far apart immune to electromagnetic noise signal carried in electromagnetic spectrum no wire bidirectional propagation environment effects: reflection obstruction by objects interference Radio types: terrestrial microwave e.g. up to 45 bps channels LAN (e.g., WiFi) 11bps, 54 bps wide-area (cellular) 3G, 4G satellite 270 msec end-end delay geosynchronous versus low altitude Introduction 1-13 Introduction 1-14 The Network Core Network Core: Circuit Switching mesh of interconnected s Two main principles: circuit switching: dedicated circuit per call: telephone net packet-switching: data sent thru net in discrete chunks bandwidth, switch capacity reserved for call no sharing Guaranteed performance call setup required Introduction 1-15 Introduction 1-16 Network Core: Circuit Switching Circuit Switching: FD and TD resources (e.g., bandwidth) divided into pieces pieces allocated to calls resource piece idle if not used by owning call (no sharing) dividing bandwidth into pieces frequency division division FD TD frequency Example: 4 users frequency Introduction 1-17 Introduction 1-18 3
Network Core: Packet Switching Packet switching each end-end data stream divided into packets user packets share resources each packet uses full bandwidth resources used as needed resource contention: demand can exceed amount available congestion: packets queue store and forward: packets move one hop at a great for bursty data resource sharing simpler, no call setup congestion: packet delay and loss protocols needed for reliable data transfer, congestion control How to provide quality of service? bandwidth guarantees for audio/video apps still an unsolved problem Introduction 1-19 Introduction 1-20 Internet structure: of s roughly hierarchical at center: small # of well-connected large s tier-1 commercial s (e.g., Verizon, Sprint, AT&T, Qwest, Level3), national & international coverage large content distributors (Google, Akamai, icrosoft) treat each other as equals Tier-1 : e.g., Sprint Tier-1 s & Content s, interconnect (peer) privately or at Internet Exchange Points s Tier 1 Tier 1 Tier 1 Introduction 1-21 Introduction 1-22 Internet structure: of s tier-2 s: smaller (often regional) s connect to one or more tier-1 (provider) s each tier-1 has many tier-2 customer nets tier 2 pays tier 1 provider tier-2 nets somes peer directly with each other (bypassing tier 1), or at Tier 1 Tier 1 Tier 1 Introduction 1-23 Internet structure: of s Tier-3 s, local s customer of tier 1 or tier 2 last hop ( access ) (closest to end systems) Tier 1 Tier 1 Tier 1 Introduction 1-24 4
Internet structure: of s a packet passes through many s from source host to destination host Tier 1 Tier 1 Tier 1 Protocol Layers Networks are complex, with many pieces : hosts s s of various media s protocols hardware, software Question: Is there any hope of organizing structure of? Or at least our discussion of s? Introduction 1-25 Introduction 1-26 Internet protocol stack ISO/OSI reference model : supporting s FTP, STP, HTTP : process-process data transfer TCP, UDP : routing of datagrams from source to destination IP, routing protocols : data transfer between neighboring elements, 802.11 (WiFi) : bits on the wire presentation: allow s to interpret meaning of data, e.g., encryption, compression, machinespecific conventions session: synchronization, checkpointing, recovery of data exchange Internet stack missing these layers! these services, if needed, must be implemented in presentation session Introduction 1-27 Introduction 1-28 message segment H t datagram H n H t frame H l H n H t source Encapsulation switch H t H l destination H l Introduction 1-29 5